In such devices or batteries the current collector generally comprises a sheet of metal, mostly based on Aluminum, to provide electrical connection to the electrolyte.
A current collector is a metallic support, the function of which is to provide to or harvest electrons from an electrode inside an electrochemical device or a photo-electrochemical device.
In devices or batteries, especially rechargeable lithium batteries, where the solid or liquid electrolyte includes a highly conductive salt such as the trifluorosulfonimide anion (TFSI−), corrosion is often observed after several cycling or at high potentials. This is mainly a localized corrosion named pitting corrosion, which induces small holes in the metal of the current collector, modifying its properties and impairing its efficiency, and consequently impairing the efficiency of the battery or device.
In order to attenuate, or at least limit, the pitting corrosion several approaches have been proposed yet.
A first approach is to modify the electrolyte composition in contact with the current collector. Numerous attempts have been made, among others:                Increasing the concentration of LiTFSI in the electrolyte of lithium-ion batteries (Kazuaki Inoue et al., “Suppression of aluminum corrosion by using high concentration of LiTFSI” in Journal of Power Sources, vol. 231, pp. 234-238, 2013);        Incorporating nanoparticles in the LiTFSI electrolyte, for instance silica fume nanoparticles (Yangxing Li et al. “Attenuation of aluminum current collector corrosion in LiTFSI electrolytes using fumed silica nanoparticles” in Electrochemical and Solid-State Letters, vol. 7, pp. A228-A230, 2004);        Adding a small amount of LiPF6 in an electrolyte containing mainly LiTFSI as lithium salt (Mouad Dahbi et al. “Comparative study of EC/DMC LiTFSI and LiPF6 electrolytes for electrochemical storage” in Journal of Power Sources, vol. 196, pp. 9743-9750, 2011);        Using ionic liquid instead of the classical organic carbonates solvents (Ethylene carbonate EC, diethylcarbonate DEC, dimethylcarbonate DMC) in the electrolyte (C. Peng et al. “Anodic behavior of Al current collector in 1-alkyl-3-methylimidazolium bis [(trifluoromethyl) sulfonyl] amide ionic liquid electrolytes” in Journal of Power Sources, no. 173, pp. 510-517, 2007).The technical solutions brought by this first approach modify the environment of the current collector. Such modifications or incorporation of additives lead to increased costs of the electrolyte.        
Another approach is to replace the aluminum current collector by a new material, for instance a flexible film made of pyrolytic polyimide graphite as disclosed by P. Han et al. “Anticorrosive flexible pyrolytic polyimide graphite film as a cathode current collector in lithium bis(trifluoromethane sulfonyl)” in Electrochemistry Communications, pp. 70-73, 2014. This material is more expensive than aluminum sheet and less easy to process. Its use severely limits the number of possible applications.
Still another approach is to coat the aluminum current collector surface with a protective layer as disclosed in WO 2005/089390 and in US 2012/0121974 which describe a lithium-ion electrochemical cell, where the cathode current collector comprising aluminum or aluminum alloy has a protective, electronically conductive coating on its surface, made of substantially pure carbon or graphite or mixed with a polymer for good mechanical properties of the coating and good adhesion of the coating to the surface of the metal foil, this last embodiment being preferred in the art. In this case (carbon+polymer), the thickness of the coating is from 0.1 μm to 10 μm. However, example 1 of US 2012/0121974 demonstrates that the protective, conductive carbon coating by itself is not sufficient to prevent corrosion of aluminum current collector, and consequently disclose in further examples the addition of LiBOB or LiPF6 to the electrolyte solution to inhibit corrosion.
Therefore the main objective of the present invention is to provide an electrochemical device or a photo-electrochemical device having a current collector with improved anti-corrosion properties, preferably without modifying the electrolyte in contact with such current collector.
Another objective of the invention is to provide an electrochemical device or a photo-electrochemical device having a current collector for electrochemical cells with improved corrosion resistance, in particular to pitting corrosion, and therefore extending the life of the device.
Another objective of the invention is to provide an electrochemical device or a photo-electrochemical device having a current collector which will be corrosion resistant and heat resistant, of low cost and easily processable.